Increased renal synthesis of ammonia from glutamine in response to metabolic acidosis is an essential component of the homeostatic regulation of acid-base balance. The time course and the magnitude of this response have been well characterized, but the genesis of this adaptation remains undetermined. Glutaminase activity is the first reaction in what is thought to be the primary pathway of rat kidney ammonia synthesis. The continued objective of this proposed research is to complete the characterization of glutaminase isoenzymes from rat kidney in conjunction with experiments designed to understand their physiological function and possible contribution to regulation of renal ammonia synthesis. Highly purified phosphate-dependent glutaminase exists in different molecular weight forms which have different kinetic properties. By studying this process we hope to determine if these changes in conformation and quaternary structure contribute to its regulation. We also plan to characterize the mitochondrial transport system for glutamine and the mechanism of increased phosphate-dependent glutaminase in response to acidosis. We have shown that the phosphate-independent glutaminase is a partial reaction of gamma-glutamyl-transpeptidase and we plan to continue the characterization of our purified preparations of this enzyme and to investigate the physiological role.